You are right, I thought I remembered someone else saying on this thread that he couldn't find a datasheet for the 7474 so I didn't look, but actually I found one quite easily!
From: Paul Koning <paulkon...@comcast.net> Sent: 16 May 2022 22:08 To: r...@jarratt.me.uk; Robert Jarratt <robert.jarr...@ntlworld.com>; cctalk@classiccmp.org Cc: Rick Murphy <r...@rickmurphy.net> Subject: Re: Replacement for a DEC 7474 Chip On May 16, 2022, at 4:59 PM, Rob Jarratt via cctalk <cctalk@classiccmp.org <mailto:cctalk@classiccmp.org> > wrote: I have several 7474s, including one marked DEC 7474. Sadly, I fear that shipping from the US is likely to be prohibitive. I have ordered some 7474s. However I am getting a bit lost in the discussion now. From a simple fan out point of view, would an S be sufficient to replace it? I can think of two ways to answer that: (1) ask and see if you get an answer, hopefullly a correct one, (2) find the data sheet for the 74x74 you're looking at, and the devices it is driving, and do the calculation. Sum up the max input currents of the driven devices, compare with the min output current of the 74x74. If the output current is >= the load current, you have the needed fanout. paul
